1. Field of the Invention
The present invention relates to joint surgery and, more particularly, to prosthetic socket components having socket openings that are adjustably positionable relative to ball components of the joints, introducers for positioning shells of prosthetic socket components on bones of the joints and systems and methods for use in joint surgery.
2. Description of the Prior Art
Various articulating joints of the body, such as the joints of the hips, have anatomical ball and socket connections between bones of the joints providing a wide range of motion. The hip joint, for instance, includes a socket or acetabulum in the pelvis and a femoral head or ball at an upper end of the femur or thigh bone received in the acetabulum. Where natural articulating joints are congenitally defective or become degraded due to disease or injury, prosthetic or artificial ball and socket components are commonly implanted in the body to replace the natural ball and socket structure of the joints. In total joint replacement surgery, prosthetic ball and socket components are both implanted as, for example, in total hip arthroplasty wherein a femoral stem component having a head or ball thereon to replace the natural femoral head is affixed to the femur, and a socket or acetabular component having a shell and a bearing insert or liner received in a cavity of the shell is affixed to the acetabulum with the head or ball of the femoral component rotatably or movably received in a socket of the liner to recreate the natural articulation of the hip joint. In subtotal or partial joint replacement surgery, natural bone structure of the joint is left intact to cooperate with an implanted prosthetic component, one example of subtotal joint replacement surgery being a cup arthroplasty wherein a prosthetic acetabular or socket component is implanted on the acetabulum to receive the natural femoral head. It is extremely important in total or partial joint replacement surgery and, in particular, total and subtotal hip replacement surgery, that the ball and socket components be optimally positioned in accordance with the physiological and anatomical features of the patient to ensure implant stability, resist dislocation and subluxation of the joint, enhance range of motion and avoid loosening or failure of the components. Accordingly, the liners of prosthetic acetabular components employed in hip surgery have been designed to protrude beyond openings to the cavities of the shells to angularly position the sockets of the liners to provide optimal coverage of the prosthetic femoral heads by the socket components to resist dislocation. U.S. Pat. Nos. 5,171,285 to Broderick, 5,169,399 to Ryland et al, 5,002,577 to Bolesky et al, 4,883,490, 4,623,352 and 4,437,193 to Oh, 4,792,337 to Muller, 4,678,472 to Noiles and 4,623,351 and United Kingdom patent 2 117 646 to Church are illustrative of acetabular components including liners having socket openings therein and shells or cups having cavities therein with openings for receiving the liners with portions of the liners angularly protruding beyond the planes of the cavity openings to angularly position the socket openings to receive a head or ball. The portions of the liners protruding beyond the planes of the cavity openings define angularly protruding lips or overhangs and, in some prosthetic socket components, the liners can be rotated relative to the shells about axes perpendicular to the planes of the cavity openings to change the position of the lips or overhangs to inhibit dislocation.
A major disadvantage of prior prosthetic socket components is that the angular distance that the liners protrude beyond the planes of the cavity openings is fixed or constant for a specified liner such that only a single size or angle of overhang can be obtained with an individual liner. Accordingly, only one size or magnitude of angle for the socket opening can be obtained with a particular liner, the angle obtained being dependent on the angle that the protruding portion of the liner defines with the plane of the cavity opening. Because the most advantageous angle for the socket opening can vary greatly among individual patients in accordance with anatomical and physiological features as determined during joint surgery, many diverse liners with different sizes or angles of overhang must typically be available during joint surgery for use as trial liners to allow a surgeon to select the best size or angle of overhang and, therefore, optimal socket opening angle, for the patient. In addition to the various trial liners, liners intended for final implantation and corresponding to the trial liners must also be available to the surgeon during joint surgery thusly necessitating a very large and costly inventory of components. Another disadvantage of prior prosthetic socket components is that the process of inserting a different trial liner in the shell for each size or angle of overhang to be considered for the patient can be tedious and time consuming and greatly impairs intraoperative flexibility. Prior prosthetic socket components have a further disadvantage in that positioning of the overhangs to resist dislocation does not produce anteversion or retroversion of the liners for increased range of motion.